1. Field of the Invention
The present invention relates to an optical information recording substrate on which visually comprehensible legible matter is formed and a method of making thereof.
2. Discussion of the Background
Conventionally, a substrate for composing an optical record disc such as a compact disc, is produced by a stamper made of a primary disc.
In such a substrate for producing an optical disc, legible matter (hereinafter a mark) is formed on an area outside of a recording area thereof, for identifying, for instance, the contents of a recording or production number. As a method of forming the mark, a method is known, for instance, wherein the mark is physically made at the inner periphery of the stamper for producing the optical information recording substrate by a punch or by a marking-off pin, or a method is known disclosed in Japanese Unexamined Utility Model Publication No. 181119/1988, wherein the mark is provided on the stamper by an ultrasonic machining.
The substrate is formed using the stamper provided with the mark, by injection molding or the like.
However, in the method of marking the mark by the conventional technology, especially when the mark is produced on the stamper by a physical method, burrs and shavings are generated, which impairs the record or the play back portion of the substrate. As the result, in the optical record disc utilizing the substrate produced by such method, errors are generated in the recording or the play back signal.
Furthermore as is described in the conventional technology, when the mark is physically produced on the stamper, a recess is generated on the surface thereof by physical force. As the result, when the substrate for the optical record disc produced by such a stamper is utilized, in forming another layer on the substrate, defects such as nonuniformity of film thickness or a cometary defect in the layer formation by spin coating method, are generated. In the case of the ultrasonic machining, it is necessary to provide a tool for the ultrasonic machining, which increases the production cost thereof.